Generally speaking rail signalling systems are designed and implemented to allow the safe passage of trains throughout the railway network. Track circuits play a major role within the interlocking as they indicate the presence of a rail vehicle and can exchange data speed information with rail vehicles. Track circuits can be divided into two groups: “jointless” track circuits and track circuits separated by mechanical insulated joints, this invention is particularly directed to the second type.
These insulated joints enable isolated sections of rails to be used as part of the track circuits.
The track circuits play a vital role, and it is therefore important to be able to identify any faulty components.
In particular if a failure of a mechanical joint occurs, the track segment won't be isolated no more, causing the signal communication between the track segment and the adjacent one. Moreover adjacent rails can be no more aligned between each other causing risk of derailments.
Consequently the track circuit will be composed by track segments in communication, bringing to dangerous and unsafe situations.
First of all it is in fact imperative that a rail break can be detected in time because it could cause a significant failure, such as a derailment, especially in the case of curved track sections.
Furthermore, if a communication between two adjacent track segments occurs, the track circuit will be unable to monitor the presence of a train in a track segment due to the impossibility to detect the shunt resistance of the train axle and wrong information on speed data can be propagated to the train.
The breakage of a mechanical joint causes drawbacks not only relating to the high-frequency signals (train detection) in the track circuit, but also relating to the low-frequency signal, because trains can acquire wrong speed data.
As it can be appreciated by the discussion above, an efficient monitoring and detection of the failure of mechanical joints covers a fundamental aspect in the safety of railway track circuits.
A possible solution is disclosed in the document EP 2216229 relating to a device for monitoring an insulated joint between sections of rail comprising a monitoring arrangement for monitoring current flow between two points along a rail in the vicinity of the rail joint by measuring voltages at the two points.
The document U.S. Pat. No. 6,779,761 describes a detection of a break in a rail by connecting the two rails together electrically with two electrical connections at opposite ends of a section of the line, causing electrical currents to flow in parallel along the two rails from a current source and detecting the currents flowing in each of the rails. From the two values of current it is possible to find if there is a break in one of the rails.
Usually the solution presented in the prior art documents relates to a method of using the effects of the changes in the track circuit introduced by the break on a testing signal.
Coded DC, or AC signals or pulsed signals are also used and they are fed to the track circuits by transmitters at one end and received by receivers at the other end of the track circuit.
Furthermore the devices and methods belonging to the state of the art provide a processing unit carrying out processing of the received signals for determining if the variations are due to a break.
Independently from the solution adopted, the known devices and methods present dedicated products to detect the breakings of mechanical joint, that must be installed in the track circuit.
The use of dedicated devices brings functional and economical drawbacks.
From a functional point of view, the addition of one or more components to the track circuit increases the possibility of failures of the track circuit and it requires more controls.
The economical drawbacks are obvious since there is an increase of costs, due not only to the purchase of a specific product, but also to the maintenance required.
Therefore, there is still the need for a track circuit in which the detection of a mechanical joint failure or breakage is integrated within the train detection function itself and therefore can be detected in an efficient way, without incurring in expensive costs and/or complex configurations using specific components added to the ones belonging to the track circuit.